Conventional wavelength division multiplexing (WDM) transmitter arrays may employ semiconductor lasers as optical transmitters. The performance of the lasers and hence the WDM systems is often judged by their wavelength stability and reach. The wavelengths of the WDM laser arrays may vary due to manufacturing process variations, device age, temperature, or other factors. Wavelength locking can facilitate signal integrity even when the lasers' wavelengths vary over time.
One approach to provide wavelength locking has been to employ a feedback system to compare actual laser output wavelength to the target laser output wavelength. Laser output can then be adjusted to correct for deviations. For discrete transmitters, a wavelength locker is used for each laser. As the number of individual optical transmitters increases, the complexity and cost for wavelength locking may also increase. What is needed is a way to provide efficient and cost-effective wavelength locking, especially in the case of transmitter arrays where one locker per laser approach is not practical. Extending the reach of a transmitter often involves extensive engineering on lasers, making the transmitters more costly. Meanwhile, inexpensive transmitters like those utilizing directly modulated lasers often have short reaches.